1. Field of the Invention
The present invention relates to a telescopically length adjustable steering column apparatus for adjusting the position of a steering wheel in the length direction of a vehicle by extending and contracting telescopically the whole length of a steering column through which a steering shaft is inserted in accordance with the physical constitution or the position of the driver.
2. Related Background Art
As a steering apparatus for a vehicle, there is a telescopically extendable and contractable steering column apparatus (a so-called telescopic steering column apparatus) for adjusting the position of a steering wheel in the length direction of a vehicle by extending and contracting telescopically the whole length of a steering column, through which a steering shaft is inserted, in accordance with the physical constitution or the position of the driver.
In the apparatus disclosed in Japanese Utility Model Application Laid-Open No. 6-78155 (Japanese Utility Model Registration No. 2588338), a lock housing portion is formed on an outer column through which an inner column is slidably inserted and a pair of movable pieces are fitted in a cylinder bore formed in the lock housing portion. That apparatus is provided with a locking mechanism for shifting the pair of movable pieces toward each other so as to press the inner column and shifting the pair of movable pieces away from each other to release the pressure on the inner column in response to swinging of an operating lever by the driver.
FIG. 4 is a side view showing the lock housing portion of the extendable steering column apparatus disclosed in Japanese Utility Model Application Laid-Open No. 6-78155 (Japanese Utility Model Registration No. 2588338). In this apparatus, the cylinder bore b formed in the lock housing portion a has a circular cross section and the pair of movable pieces c slidably fitted in the cylinder bore also have circular cross sections correspondingly.
However, in the apparatus disclosed in Japanese Utility Model Application Laid-Open No. 6-78155 (Japanese Utility Model Registration No. 2588338), since the lock housing portion a has a circular cross section and the pair of movable pieces c also have circular cross sections, in the case that a torque is exerted on the movable piece c when the operating lever is swung, the movable piece is sometimes rotated.
In the case that the movable pieces c has been rotated due to swinging of the operating lever, the movable piece may bite the inner column at the time of adjustment of the telescopic position.
In addition, in the case that the cross sections of the cylinder bore b and the movable pieces c are circular, the pressing surfaces (or the friction surface) in which the movable pieces c press the inner column are unstable, so that the pressing force (or the holding force) as a frictional force becomes unstable.